Simplified Equations to Estimate Flushline Diameter for Subsurface Drip Irrigation Systems

Abstract. A formulation of the Hazen-Williams equation is typically used to determine the diameter of the common flushline that is often used at the distal end of subsurface drip irrigation systems to aid in joint flushing of a group of driplines. Although this method is accurate, its usage is not intuitive and can be confusing since designers must only consider the portion of flows reaching the flushline. Earlier alternative methods provided simple flushline diameter guidelines related to the cross-sectional areas of the flushline and the driplines contributing flow to it. Improvements to these alternative guidelines and their accuracy with respect to the full Hazen-Williams formulation are reported here in both SI and English units to aid in their usage. The improved equations are accurate and tend to self-regulate their accuracy over the range of typical SDI system design parameters. The authors recommend that these equations be used in concert with the full Hazen-Williams formulation for improved quality assurance in flushline design for SDI systems.